The invention relates to a control method for an integrated circuit formed with a common switching electrode for at least two oppositely switchable transistors, which are operative in the integrated circuit for transferring an information charge or for resetting, respectively. A connection of the switching transistors is coupled to a capacitance for picking up the information charge and for resetting under the transistor control of a clock pulse signal occurring at the switching electrode. The invention also relates to a device suitable therefor.
An integrated circuit of this type may form part of a more complex integrated circuit suitable for use in, for example, television. A frame transfer device operating as an opto-electronic solid-state charge transfer sensor whose data is mentioned under numbers NXA1010 and NXA1020 in a Philips data handbook is mentioned as an example. The sensor comprises, in a semiconductor body, a pick-up member, an information storage member and a parallel-in, series-out shift register member comprising three output shift registers. The circuit comprising the two switching transistors and the common switching electrode is present at the output of each of the three output shift registers. The charge transfer transistor is the last in the shift register row of such transistors, while the required charge is supplied via the reset transistor for periodically resetting the capacitance charges at the charge transfer transistors in the row. Under the control of three 120.degree. phase-shifted clock pulse signals the three output shift registers, likewise shifted in phase, are operative with the charge transfer transistors and the associated reset transistor. By using the common switching electrode a resetting of the last capacitance charge in the row effected via the reset transistor is succeeded by an information charge transfer from the next-to-last capacitance.
The picture signal supplied by the output shift register by means of the described control method is supplied for further signal processing operations in the described sensor via a signal amplifier which is also integrated. Due to the control method, the picture signal occurs with a pulse shape caused by cross-talk from the switching clock pulse signal, while the reset pulse level only comprises noise and the signal pulse level comprises picture information with noise. To remove the cross-talk clock pulse and to obtain a continuous picture signal, this is applied in known manner to a series arrangement of a clamping circuit for fixing the reset pulse level and a subsequent signal sample-and-hold circuit operating at the signal pulse level. After the desired further signal processing operations the picture signal can be applied for display to a picture display device, either (or not) after storage in a signal recording and display device.
The advantages of the fact that the switching electrode for the last charge transfer transistor in the shift register row and the reset transistor are common are the absence of an extra electrode connection to the integrated circuit for the supply of a separate reset clock pulse signal on the one hand and the supply electrode region on the semiconductor body required for this purpose in the integrated circuit on the other hand. In the embodiment described, comprising the three output shift registers, three extra electrode connections and associated supply electrode regions would be required on the semiconductor body. Both the lack of space for the three extra electrodes and the additional costs involved for each electrode connection leads to the embodiment with the common switching electrode.
It is found in practice that when picking up a picture with low light levels the picture signals for display obtained with the described sensor and control method may have an unacceptable noise level. When the picture signal is displayed, dark scene parts show disturbing noise which is less conspicuous in bright scene parts.